Conventionally, a flow rate control unit represented by a pressure type flow controller known as a nozzle diagnostic mechanism can diagnose abnormality of a flow channel narrowing nozzle and a piping system constituting a flow channel located on a downstream side of the nozzle.
This kind of nozzle diagnostic mechanism comprises a control section that makes it possible to diagnose an inside flow channel narrowing nozzle by reading a time dependent change of a gas pressure value inside the flow channel in conjunction with an open/close movement of a close valve and a flow rate adjusting valve at a time of self-diagnosis in a state that the flow rate adjusting valve is closed and the close valve is open.
Then, in the case that no abnormality exists in the gas flow channel, a curve line of the time dependent change of the gas pressure value measured at a time of conducting a self-diagnosis (t=0˜Δt) such as a nozzle clog describes a curve line that almost overlaps a specified value. On the contrary, in the case that the flow channel narrowing nozzle is clogged, a descending speed of an initial pressure slows from a start (at a time t=0) of the self-diagnosis time as shown in a virtual line. More specifically, at a time when the time dependent change curve line of the gas pressure is abnormal, it can be known that the abnormal curve line is attributed to the clogged nozzle (refer to patent document 1).    Patent document 1: Japan patent laid-open number 2000-214916